This invention relates to an improved process for preparing polyarylene polyethers. The polyarylene polyethers produced by the precess of this invention are low in color.
Poly(arylene polyether) resins are tough, rigid, high strength thermoplastics which maintain their properties over a wide temperature range of from -150.degree. F. to above 300.degree. F. They have a high continuous use temperature of about 300.degree. F. They are hydrolytically stable and have excellent mechanical and electrical properties which allows them to be molded into a variety of articles.
There are several methods for preparing polyarylene polyethers. For example, U.S. Pat. Nos. 4,108,837 and 4,175,175 describe the preparation of polyarylene polyethers, and in particular, polysulfones. Several one-step and two-step processes are described in these patents. In these processes, a double alkali metal salt of a dihydric phenol is reacted with a dihalobenzenoid compound in the presence of sulfone or sulfoxide solvents under substantially anhydrous conditions.
In a two-step process, a dihydric phenol is first converted, in situ, in the presence of a sulfone or sulfoxide solvent to the alkali metal salt by reaction with an alkali metal or alkali metal compound. After removing water, a dihalobenzenoid compound is reacted with the double salt. Further, the alkali metal salt of the dihydric phenol may be added in the solvent to the dihalobenzenoid compound either continuously, incrementally or all at once to achieve the polymerization reaction. Several other variations of the process are described in the patents.
However, the polyarylene polyether polymers produced by said processes tend to have a high color which precludes their use in several applications.
It has been found that the sulfone or sulfoxide solvent can undergo side reactions with the dihydric phenol and the alkali metal or alkali metal hydride, hydroxide, alkoxide or alkyl compounds which imparts color to the polymer. Additionally, the sulfone and sulfoxide solvent can decompose under reaction conditions to produce colored products. For example, under the reaction conditions of producing polyarylene polyethers, the dimethyl sulfoxide solvent can decompose to formaldehyde, dimethyl sulfide, dimethyl disulfide and other products, all of which impart color to the polymer.
However, the sulfone and sulfoxide solvents are particularly effective in preparing polyarylene polyethers since they are good solvents for the alkali metal salts of the dihydric phenols. Therefore, a need exists to eliminate or substantially reduce the side reactions and decomposition of these solvents. Such elimination or reduction would produce polyarylene polyether polymers which are low in color.